Electromigration is the transport of material caused by the gradual movement of ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms. The effect of electromigration is an important consideration to take into account in applications where high direct current densities are used, such as in microelectronics and related structures. In fact, electromigration is known to decrease the reliability of integrated circuits (ICs) and hence lead to a malfunction of the circuit. In the worst case, for example, electromigration leads to the eventual loss of one or more connections and intermittent failure of the entire circuit.
The effect of electromigration becomes an increasing concern as the size of the IC decreases. That is, as the structure size in ICs decreases, the practical significance of this effect increases. Thus, with increasing miniaturization the probability of failure due to electromigration increases in VLSI and ULSI circuits because both the power density and the current density increase.
Back-end-of-line (BEOL) interconnects, consisting of metal wires and inter-level vias, carry high direct current (DC) in advanced integrated circuit (IC) chip technology. In particular, as IC chip technology advances, the current density required in these metal wires/vias increases with the ever-decreasing dimensions in IC chip technology. Also, self-heating by high current devices raises the temperature of nearby interconnects under circuit operation and makes use of high current carrying BEOL interconnects extremely challenging. For example, a device that uses high current and self-heats (e.g., a resistor, a bipolar transistor, etc.) may heat up an interconnect wire that couples to the device. The high current leads to electro-migration (EM) degradation of the interconnect (via and/or line), causing shorts or opens.
As a result, the current-carrying capability (or the Idc limit specified in the design manuals) is significantly reduced to avoid electro-migration degradation in interconnects. As an example, a direct current limit in a copper interconnect may be reduced by a factor of more than three resulting from a temperature rise of about 15° C. from, for example, 85° C. to 100° C., and by almost a factor of 20 at a 125° C. interconnect temperature. As a result, high direct current at elevated temperatures is almost impossible with conventional interconnect structures.
There are various methods aimed at addressing this reliability issue in metal wires/vias. Known methods, though, result in EM induced voids occurring in any section of the segment, which will cause the wire to eventually open as the void grows in size. Other methods use liners to enclose vias. However, such structures and methods do not provide any means to protect EM damage in metal wires, nor do such structures address the EM damage at the via/wire interface.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.